The present invention generally relates to bright zinc electroplating and, more particularly, to electroplating baths for zinc plating which include bath soluble polymers containing repeating tertiaryaminoalkyl acrylamide groups, or quaternary salts thereof, which produce bright, zinc electrodeposits and which, moreover, permit the plating to be conducted with various concentrations of cyanide salts or even desirably in the total absence of said salts.
Conventionally, zinc electroplating has been conducted in plating baths employing alkali metal cyanide salts such as, for example, sodium cyanide which serves in such baths as an additive or complexing agent to achieve the desired plating operation and produce bright, smooth grained, zinc deposits.
Quite often, the brightness and/or grain of the electrodeposit is not entirely suitable for many plating applications and, accordingly, various additives such as brighteners or grain refiners have been required in the bath in order to enhance the plating. Such additives have not, however, always been effective in their intended use, and typically have also required high levels of cyanide in order to achieve the desired plating. Moreover, because of the toxicity of cyanides and, more recently, by reason of the environmental considerations adversely affecting the economic employment of these cyanides, other plating methods have been sought which operate effectively either at a low cyanide level or advantageously in the total absence of cyanide salts.
Heretofore, a wide variety of procedures and additives have been proposed for use in zinc plating for the purpose of eliminating the need for cyanides or at least lessening the concentration thereof required. Many of these additives employ an alkaline plating bath system utilizing an alkali metal or sodium zincate combined with various additives such as polyamines to achieve the desired bright zinc deposit and a smooth or fine grained, mirror-like surface.
While certain of these alkaline systems do avoid the use of cyanides or at least high bath concentrations of cyanide, they generally have not been overly successful, and the zinc electrodeposits typically produced have been characterized by a number of deficiencies such as a dull or granular finish which render them of less than acceptable commercial value. Such systems, moreover, typically lack the desired capability of producing a suitable smooth, mirror-like deposit over a broad current density range and generally are especially ineffective at lower current density ranges which conventionally occur in many commercial plating operations.
It has now been discovered that bath soluble polymers containing repeating tertiaryaminoalkyl acryamide groups, or quaternary salts thereof, may be employed in alkaline zinc electroplating baths to produce fine grained, bright zinc deposits over a broad current density range both in the presence and absence of cyanide salts. In this regard, it has also been discovered that the effectiveness of such polymers can be enhanced using, in conjunction therewith, certain polyethylenepolyamines, particularly those formed by reacting ammonia with ethylene dichloride, or quaternary salts thereof.
It is, therefore, a general object of the present invention to provide an alkaline, zinc electroplating bath which achieves bright zinc deposits either with various concentrations of cyanide salts or in the absence thereof.
Another object of the present invention is to provide an improved alkaline, zinc or electroplating bath additive composition which is particularly suited for cyanide zinc barrel plating operations and which is characterized by improved throwing power at high cathode efficiencies and produces brilliant deposits over a wide current density range.
Another object of the present invention is to provide an alkaline, zinc electroplating bath which employs a bath soluble polymer containing repeating tertiaryaminoalkyl acrylamide groups.
Another object of the present invention is to provide an alkaline, zinc electroplating bath which employs a bath soluble polymer containing repeating quaternaryaminoalkyl acrylamide groups.
Another object of the present invention is to provide an alkaline, zinc electroplating bath which employs a bath soluble polymer containing repeating tertiary or quaternary-aminoalkyl acrylamide groups in admixture with a polyethylene-polyamine such as, for example, one prepared by reacting ammonia with ethylene dichloride, or a quaternary salt thereof.
Another object of the present invention is to employ such polymers which contain repeating tertiary or quaternary-aminoalkyl acrylamide groups with other conventional plating additives such as brightening agents and grain refiners to achieve bright, mirror-like zinc deposits over a broad current density range.
Another object of the present invention is to provide a method of zinc electroplating employing such improved bath which is capable of effectively operating in a commercially desirable manner both with and without cyanide salts.
These and other objects of the present invention will be apparent from the following further detailed description thereof.